Currently, the cancer rates are greatly increased and are in a “blowout”. The WHO international cancer research center has announced a “world cancer report” said, according to the current trend of cancer, in 2020, the world cancer rates will increase 50% than now, global new cancer cases every year there well be up to 15 million people. Thus, to develop a simple, rapid, sensitive and effective method for cancer labeling is becoming more and more urgent. At present, methods for cancer labeling are X-ray detection technology, ultrasonic technology, CT detection technology, magnetic resonance (MRI) testing technology, infrared thermal image detection technology, near infrared scan detection technology, PET-CT detection technology and so on. However, the above-mentioned methods have the following disadvantages in practical imaging applications: lack of specificity for imaging, with large radiation damage, cannot diagnose the cancer by independent labeling, unable to deep imaging for tumors and so on. The optical molecular imaging fluorescence labeling technique overcomes latter's problems of these methods mentioned above. The relevant commercial fluorescent dyes, such as phenanthridine derivative (EB, PI), acridine (AO), imidazoles (Hoechst, DAPI), cyanine dyes (Cy, TOTO, SYTO) and so on, play an important role in the areas of the genomics technology, nucleic acid quantitative testing and blood cell analysis. However, the fluorescent dyes/probes for specific cancer labeling are lacking.
In recent years, with the development of two-photon technique, the two-photon fluorescence microscope has become most important imaging tools in the study of life sciences. Compared with single-photon fluorescence confocal microscope, the two-photon fluorescence microscope has significant advantages, including near-infrared excitation, dark-field imaging, reduced photodamage and photobleaching, high lateral resolution and vertical resolution, reduced absorption coefficient of biological tissues, so on. (Helmchen F, Svoboda K, Denk W et al. Nature, 1999, 2:989-996. Maiti S, Shear J B, Williams R M et al. Science, 1997, 275:530. Ventelon L, Charier S, Moreaux L et al. Angewandte Chemie International Edition, 2001, 40: 2098). The two-photon fluorescence imaging technique provides a new platform for biological imaging. Regrettably, two-photon fluorescence probes for the imaging of tumor in vivo are rarely reported. So, exploring novel two-photon fluorescence probes having a good labeling specificity for cancer is the key to achieve two-photon imaging of tumors.